Dean Bubley: VoIP + SMS = headaches.

"So... if you are looking to hybridise VoIP and cellular, on single- or dual-mode phones, for consumers or enterprise, with wVoIP or circuit-to-VoIP-gateway, you need to have a good SMS story. And a good SMS user experience. It's one of the major flaws in many of the current SIP-based dual-mode WiFi offers, and perhaps UMA's only redeeming positive feature."